Field of the Invention
The present invention relates to an image forming apparatus such as a multifunction apparatus.
An image forming apparatus forms an image on a recording medium using an electrophotographic image forming process. Examples of image forming apparatuses include an electrophotographic copying machine and an electrophotographic printer.
A developing unit means a unit that integrates developer, a developer storage portion, a developer bearing member, and the like disposed in an image forming apparatus and develops a developer image from an electrostatic image.
Description of the Related Art
Japanese Patent Laid-Open No. 2001-242690 discloses an image forming apparatus that detects abnormalities of a toner agitation unit on the basis of the range of fluctuation of the capacitance between a plurality of electrodes that periodically fluctuates owing to the rotation of the toner agitation unit.
Japanese Patent Laid-Open No. 2007-233103 discloses an image forming apparatus in which, in the process in which toner in a toner storage chamber decreases, a case where the range of fluctuation of capacitance changes from small to large and then to small is a case where the toner remaining amount is small, and that resets the reference value for calculating the remaining amount of toner when this phenomenon is detected.
Japanese Patent Laid-Open No. 8-292634 discloses a toner cartridge in which a sealing sheet sealing an opening between a toner storage chamber and a developing chamber is attached to an agitating member, and, after the sealing sheet is torn from the opening when a developing unit is used, the sealing sheet rotates together with the agitating member. It can be thought that, after that, this sealing sheet can also agitate developer as with the agitating sheet by rotating together with the agitating sheet.
In a situation in which there are such technologies, problems still remain in a configuration for detecting the remaining amount of developer by detecting capacitance. In the case of Japanese Patent Laid-Open No. 8-292634, the sealing sheet in the toner storage chamber attached to the main body of the apparatus may deteriorate under a severe usage environment such as an environment in which the image forming apparatus performs printing operation continuously for a long period under a high-temperature environment.
The Young's modulus of the sealing sheet (sheet member) decreases due to deterioration (the sealing sheet loses stiffness), and the sealing sheet plastically deforms so as to wrap itself around the agitating shaft (this deteriorated state will be hereinafter referred to as settling). In this case, the sealing sheet covers the agitating shaft and agitating member, and toner is less likely to enter the inside of the sealing sheet, and the bulk density of toner decreases accordingly. As a result, the capacitance of developer may be detected low compared to the actual toner amount.